The Probability of Making a Type I Error

The level of significance, ,  is the probability of making a type I error

The level of significance which is actually the probability of making Type I Error (rejecting the null hypothesis though it is true) is usually preset by the statistical analyst before the sample data are taken.

If sever damages can happen because of the Type I Error, then choose a small probability of making the type I error or a small level of significance. That means you must allow only a small chance of doing Type I Error or its probability so that sever damages can follow only to a small chance of making Type I Error.

If the sever damages are not possible because of Type I Error, then you can set a higher probability of Type I Error or significance level.

P (Type I Error) = level of significance = α

The consequence of a small α is large β.

Be careful, (1-β) is not α

because (1-β) = the power of the test.

DNA Pot (c) 2009 - Current

Level of significance = = P (Type I Error)